Turbocharging an engine allows the engine to provide power similar to that of a larger displacement engine while engine pumping work is maintained near the pumping work of a normally aspirated engine of similar displacement. Thus, turbocharging can extend the operating region of an engine. Turbochargers function by compressing intake air via a compressor driven by a turbine operated by exhaust gas flow. The amount of compression provided by the turbocharger (referred to as boost pressure) may be regulated by adjusting the position of a wastegate coupled across the turbine, based on feedback from a throttle inlet pressure (TIP) sensor positioned in the intake upstream of the throttle and downstream of the compressor.
If the throttle inlet pressure sensor is degraded, for example if the throttle inlet sensor is stuck in range and is outputting a constant signal even as throttle inlet pressure changes, the engine boost pressure control routine may continue to adjust the position of the wastegate even after target boost pressure has been achieved. Under some conditions, this may result in engine knock and/or engine damage if the wastegate continues to be moved to a more closed position than indicated and thus the intake air is compressed more than desired.
The inventors herein have recognized that standard throttle inlet pressure sensor diagnostics can take a relatively long time to recognize throttle inlet pressure sensor degradation. During the time that the diagnostic routine is being executed, overboost conditions may occur leading to engine knock and/or engine damage. Accordingly, a method is provided to at least partly address the issues with the above approach. In one embodiment, a method for an engine having a throttle comprises, if an inferred throttle inlet pressure (TIP) value is different than a measured TIP value, adjusting a wastegate of a turbocharger based on the inferred TIP value and not based on the measured TIP value, the inferred TIP value based on air flow through the throttle, throttle angle, and manifold absolute pressure (MAP).
In this way, an inferred TIP value may be estimated based on engine operating parameters other than the actual throttle inlet pressure. The inferred TIP value may be substituted for the measured TIP value if the values differ, until the TIP sensor diagnostic routine detects degradation of the TIP sensor. By doing so, engine knock and/or damage that may occur before the diagnostic routine detects degradation of the TIP sensor may be avoided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.